/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification of Java bytecode.
 *
 * Copyright (c) 2002-2018 GuardSquare NV
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.classfile.visitor;

import proguard.classfile.*;

/**
 * This <code>ClassVisitor</code> delegates its visits to another given <code>ClassVisitor</code>, but only for
 * functional interfaces, that is, interface classes that have exactly one abstract method.
 *
 * @author Eric Lafortune
 */
public class FunctionalInterfaceFilter implements ClassVisitor {
    private final ClassVisitor classVisitor;

    /**
     * Creates a new ProgramClassFilter.
     * 
     * @param classVisitor the <code>ClassVisitor</code> to which visits will be delegated.
     */
    public FunctionalInterfaceFilter(ClassVisitor classVisitor) {
        this.classVisitor = classVisitor;
    }

    // Implementations for ClassVisitor.

    public void visitProgramClass(ProgramClass programClass) {
        if (isFunctionalInterface(programClass)) {
            classVisitor.visitProgramClass(programClass);
        }
    }

    public void visitLibraryClass(LibraryClass libraryClass) {
        if (isFunctionalInterface(libraryClass)) {
            classVisitor.visitLibraryClass(libraryClass);
        }
    }

    // Small utility methods.

    private boolean isFunctionalInterface(Clazz clazz) {
        // Is it an interface?
        if ((clazz.getAccessFlags() & ClassConstants.ACC_INTERFACE) == 0) {
            return false;
        }

        // Count the abstract methods in the interface hierarchy.
        // Subtract any corresponding default methods, since only abstract
        // methods that don't have a default implementation count.
        // TODO: Find a better way to count default methods, since there may be more of them for a single abstract
        // method, or we can find one via different paths.
        MemberCounter abstractMethodCounter = new MemberCounter();
        MemberCounter defaultMethodCounter = new MemberCounter();
        clazz.hierarchyAccept(true, false, true, false,
            new AllMethodVisitor(new MemberAccessFilter(ClassConstants.ACC_ABSTRACT, 0,
                new MultiMemberVisitor(abstractMethodCounter, new SimilarMemberVisitor(clazz, true, false, true, false,
                    new MemberAccessFilter(0, ClassConstants.ACC_ABSTRACT, defaultMethodCounter))))));

        return abstractMethodCounter.getCount() - defaultMethodCounter.getCount() == 1;
    }
}
